High energy screed for a paver or the like

ABSTRACT

The trailing portion of the screed is connected to the draft arms by leaf springs contained in a vertical transverse plane. The upper ends of the springs are rigidly secured to the draft arms; the lower ends of the springs are connected to the screed by a horizontal, transverse pivot. Vibrators are mounted on the screed adjacent the leading portion thereof. Vertically disposed coil springs have their lower ends engaged with the vibrators for imparting a downward force thereto. The upper ends of these springs support weights, which weights are freely supported by vertical walls mounted from the draft arms.

United States Patent Lehman et al.

[ HIGH ENERGY SCREED FOR A PAVER OR THE LIKE Filed:

Inventors: Herbert A. Lehman, Aurora; Fred T. Smith, Dearborn Heights, both of Mich.

Assignee: Barber-Greene Company, Aurora,

Nov. 21, 1972 Appl. No.: 308,535

References Cited UNITED STATES PATENTS Barber Jackson 404/114 Jackson 404/113 Jackson 404/113 Primary Examiner-Nile C. Byers, Jr. Attorney, Agent, or Firm-McDou;gall, Hersh & Scott [5 7] ABSTRACT The trailing portion of the screed is connected to the draft arms by leaf springs contained in a vertical transverse plane. The upper ends of the springs are rigidly secured to the draft arms; the lower ends of the springs are connected to the screed by a horizontal, transverse pivot. Vibrators are mounted on the screed adjacent the leading portion thereof. Vertically disposed coil springs have their lower ends engaged with the vibrators for imparting a downward force thereto. The upper ends of these springs support weights, which weights are freely supported by vertical walls mounted from the draft arms.

10 Claims, 2 Drawing Figures HIGH ENERGY SCREED FOR A PAVER OR THE LIKE BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has particular, although not exclusive, application to asphalt pavers and the like, and more particularly to screeds which form part of such equipment. As is known to those skilled in the art, screeds of this type are usually provided with vibrating mechanism for compacting the asphalt material distributed by the paver so as to form a lift or mat of asphalt pavement material.

2. The Prior Art Screeds of the type under consideration are provided with the vibrating mechanism so as to impart a gener ally vertical oscillating or reciprocating movement to the screed. This vibrating mechanism is most often in the form of eccentric weights rotated about horizontal transverse shafts. In these prior art screed devices, the vibratory movement is imparted to the screed generally uniformly throughout the entire length and width thereof. As is known to those skilled in the art, the screed itself cannot compact the asphalt material to the extent required. Consequently, compaction vehicles, which include large and heavy rollers, follow the paver to compress the asphalt lift or mat to an extent greater than that achieved by the paver.

SUMMARY AND OBJECTS OF THE INVENTION The present inventionrelates to a new and improved high energy vibratory screed which permits greater compaction of the asphalt lift or mat than that heretofore attainable. The present invention minimizes the amount of rolling by compaction devices and also al lows the construction of thicker lifts or mats, thereby reducing the number of passes of the paver of finisher to achieve the total pavement thickness required.

A primary object of the present invention is the provision of a new and improved high energy vibratory screed for a paver or the like.

Another object of the present invention is the provision of a new and improved screed for a paver or the like, wherein the amount of vertical vibratory movement of the screed progressively decreases from the leading portion to the trailing portion thereof.

Still another object of the present invention is the provision of a vibratory screed of the type described, wherein the trailing portion of the screed is connected to the draft arms by yieldable transverse pivot means and wherein the vibrating mechanism is connected to the screed adjacent the leading portion thereof such that vertical orbital vibrating movement is imparted to the screed, the amount of vertical vibratory movement of the screed progressively decreasing from the leading portion to the trailing portion thereof.

Another object of the present invention is the provision of a screed of the type described wherein vertically disposed springs have their lower ends engaged with the vibrating mechanism so as to impart downward forces thereto, the upper ends of these springs being in supporting engagement with weights freely supported by vertical wall means mounted from the draft arms.

These and other objects and advantages of the invention will become apparent from the following specification disclosing a preferred embodiment shown in the accompanying drawings.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevational view of a screed embodying the present invention, such screed being shown mounted from the rear ends of the draft arms of an asphalt paver or finisher; and

FIG. 2 is a partial section taken along the line 2--2 of FIG. 1.

DESCRIPTION OF A PREFERRED EMBODIMENT An asphalt paver or finisher of a type well known to those skilled in the art is partially illustrated in FIG. I and generally designated 10. The paver includes the usual pair of draft arms, one of such draft arms being illustrated and designated 12. The paver 10 includes a pair of longitudinally disposed material handling conveyors (not shown) for moving the asphalt material rearwardly for lateral distribution by transverse screw augers, one of such augers being shown in phantom lines and designated 14. The draft arms 12 mount a vibratory screed assembly, generally designated 15, which screed assembly compacts the material into a lift or mat as will be explained herein.

A horizontally disposed transverse tube 16 has its respective opposite ends journaled in annular support members, the latter being mounted from the draft arms; one of such support members is illustrated and designated 17. It will be understood that the tube 16 is mounted for rotation about its longitudinal axis to permit changing of the angle of attack of the screed for controlling the level of the screed in a manner well known to those skilled in the art. The tube 16 mounts a depending strike-off plate 18. Preferably. means (not shown) are provided to permit vertical adjustment of the strike-off plate 18.

With reference to FIG. 2, which illustrates the righthand portion of the screed assembly 15, it should be mentioned that such screed assembly is symmetrical with respect to its longitudinal centerline. Accordingly, the description of the parts illustrated in FIG. 2 applies fully to the left-hand portion of the screed which is not illustrated.

A pair of parallel, spaced, vertically disposed plates 20, 21 have their forward ends secured to the tube 16. The plate 20 mounts a bracket plate 23, which plate pivotally mounts a journal member 24, the latter rotatably receiving one end of an adjustment screw 25. This adjustment screw, which includes a hand crank 26, is

threadingly engaged with a block 27, which block is pivotally carried by the draft arm 12. Accordingly, it is apparent that rotation of the hand crank 26 will rotate the screed about the longitudinal central axis of the tube 16 so as to vary the angle of attack of the screed.

is constituted by a plurality of leaf springs contained in vertical transverse planes.

The screed assembly further includes a screed 35 in the form of a hollow compaction box having a compaction surface 35a. The lowermost leaf spring 33a of each spring assembly is connected with the trailing portion of the screed by a pivot assembly 37, which assembly includes a horizontally and transversely disposed pivot pin 37a. It will be understood that the screed is mounted for pivoting movement about a horizontal transverse axisdefined by coaxially aligned pivot pins 37a. By reason of the leaf spring assemblies. it is apparent that limited horizontal movement of the pivot pins 37a will be permitted upon operation of the vibrating means to be described below. At this time it should be mentioned that the pivot assemblies 37, which are connected to the screed adjacent the trailing portion thereof, constitute the sole means for transferring longitudinal draft forces to the screed from the draft arms 12.

Plural vibrators are mounted on the upper portion of the screed adjacent the leading portion thereof. The vibrator 40 includes a journal 41 receiving a transversely extending shaft 42. An eccentric weight member 43 is fixedly mounted to the shaft adjacent each of the journals 41. Power means (not shown) impart rotation to the shaft 42 thereby to generate vibratory movement by reason of the eccentric weights 43.

The vibrator 40 includes a housing structure 45. A vertically disposed coil spring 46 has the lower end thereof engaged with this housing structure. A weight 47 rests on the upper end of the coil spring 46. This weight is movably or freely contained within a cavity defined by the plates 20, 21 and transversely disposed plates 48, 49, the latter plates being mounted between the plates 20, 21.

Referring to FIG. 2, a vibrator 50 is identical to the vibrator 40 just described. The vibrator 50 includes a journal 51 for the shaft 42 and an eccentric member 52 mounted on the shaft. The housing structure 53 is engaged by the lower end of a coil spring 54, which spring supports a weight 55. Again, this weight is freely contained within a pocket or cavity defined by the plates 29, 30 and by a pair of plates (not shown) extending between the plates 29, 30.

In use, rotation is imparted to the shaft 42 for activating the vibrators. The centrifugal forces developed during the upward movement of the eccentrics on the shaft 42 are stored in the springs 46, 54 these spring forces are released during the down stroke of the eccentric weights and are additive to the centrifugal forces developed by the eccentrics. This additional energy stored in the springs during the up stroke and released during the down stroke results in the development of a compacting force greater than that obtainable by the eccentric weights alone. Accordingly, the use of such springs greatly increases the efficiency of the screed in compacting the asphalt material.

The vibrators impart horizontal oscillating movement to the screed as well as vertical oscillating movement. The leaf springs 33 permit the screed to oscillate horizontally; however, these springs permit only a very limited amount of vertical vibratory movement to the trailing portion of the screed. On the other hand, the leading portion of the screed is free to move in response to both the horizontal and vertical oscillating movements or forces generated by the vibrators.

The vibrators 40, cooperate with the leaf spring assemblies 33 such that the leading portion of the screed has a vibratory movement in the form of vertical orbital movement indicated by the arrows 60, such movement being contained in a vertical longitudinal plane. This cooperating effect of the vibrating mechanism and the leaf springs cause the trailing portion of the screed to have similar vertical orbital movement, except that the amount of vertical vibratory movement of the trailing portion of the screed is substantially less than the amount of vertical vibratory movement of the leading portion of the screed. This orbital movement of the trailing portion of the screed is indicated by the arrows 61.

It should be apparent that the amount of vertical vibratory movement of the screed progressively decreases from the leading portion of the screed to the trailing portion thereof. It is believed that this feature contributes substantially to the increased efficiency of the screed assembly according to the present invention. The reason for this is that successive increments of material beneath the screed receive progressively lesser amounts of vertical displacement from the screed for each stroke thereof. This increased efficiency also obtains because the amplitude of vertical movement of the leading portion of the screed is not limited, as is the case in conventional screeds; therefore, all of the kinetic energy developed by the vibrating mechanism can be released into or transferred to the material being compacted.

Since the present invention provides for greater compaction of the material, the amount of subsequent rolling is substantially reduced. Further, the present invention permits the construction of thicker lifts or mats and thereby reduces the number of passes of the finisher or paver to achieve the total pavement thickness required.

It will be readily apparent to those skilled in the art that the screed assembly according to the present invention is readily adaptable for automatic grade and slope control; such an automatic system is shown in Munyon Patent 3,285,148 assigned to the assignee of the present invention. Further, the screed assembly of the present invention will preferably be provided with crown adjustment or control mechanism well known to those skilled in the art.

We claim:

1. In a vibratory screed assembly for a paver or the like, the improvement comprising:

a. a frame;

b. a screed having leading and trailing portions;

c. mounting means connecting the trailing portion of the screed with the frame for relative vibratory movement therebetween, said mounting means being defined by spring means which serve as the sole means for transferring draft forces from the frame to the screed;

d. vibrating means connected to the leading portion of the screed;

e. said mounting means and said vibrating means cooperating with each other to impart vibratory motion to the screed characterized by:

l. at least vertical oscillatory movement of the leading portion of the screed;

2. predominantly horizontal longitudinal movement of the trailing portion of the screed; whereby the amount of vertical vibratory movement of the screed progressively decreases from the leading portion to the trailing portion thereof.

2. In a vibratory screed assembly for a paver or the like, the improvement comprising:

a. a frame;

b. a screed having leading and trailing portions;

0. mounting means connecting the trailing portion of the screed to the frame, said mounting means being defined by yieldable means which are substantially inextensible in a vertical direction and which therefore permit movement of the trailing portion of the screed in a horizontal plane and restrain movement of said trailing portion in a vertical plane;

d. vibrating means engaged with the screed adjacent the leading portion thereof;

e. said mounting means and said vibrating means co operating with each other to impart vibratory motion to the screed characterized by:

l. orbital movement of the leading portion of the screed as considered in a vertical longitudinal plane;

2. orbital movement of the trailing portion of the screed as considered in a vertical longitudinal plane, the amount of vertical vibratory movement of the trailing portion of the screed being substantially less than the amount of vertical vibratory movement of the leading portion of the screed;

whereby the amount of vertical vibratory movement of the screed progressively decreases from the leading portion to the trailing portion thereof.

3. The improvement according to claim 2 wherein said vibrating means includes a vibratory mechanism mounted on the leading portion of the screed and including an eccentric element supported for rotation about a horizontal transverse axis, and spring means engaged with said vibrating mechanism for transferring a vertical downward force to the latter.

4. The improvement according to claim 3 wherein said vibrating means further includes a weight engaged with said spring, said weight being carried by said frame for vertical movement relative thereto.

5. The improvement according to claim 2 wherein said yieldable means include plural leaf springs generally disposed in a vertical transverse plane, said springs having their upper ends fixed to said frame and their lower ends connected to the trailing portion of the screed by transverse horizontal piivot means.

6. In a vibratory screed assembly for a paver or the like, the improvement comprising:

a. a frame;

b. a screed having leading and "trailing portions;

c. mounting means connecting the trailing portion of the screed to the frame and permitting at least rocking movement of the screed about a horizontal transverse axis disposed adjacent said trailing portion, said mounting means being defined by spring means which serve as the sole means for transferring draft forces from the frame to the screed;

d. vibrating means connected to the leading portion of the screed;

e. said mounting means and said vibrating means cooperating with each other to impart vibratory rocking movement of said screed about said axis, whereby the amount of vertical vibratory movement of the screed progressively decreases from the leading portion to the trailing portion thereof.

7. The improvement according to claim 6 wherein said mounting means engages said. screed adjacent only the trailing portion thereof and constitutes the sole means through which longitudinal draft forces are transferred from said frame to said screed.

8. The improvement according to claim 7 wherein said vibratory means engages said screed adjacent only the leading portion thereof.

9. The improvement according to claim 8 wherein said vibrating means includes a vibratory mechanism mounted on the leading portion of the screed and including an eccentric element supported for rotation about a horizontal transverse axis, and spring means engaged with said vibrating mechanism for transferring a vertical downward force to the latter.

10. The improvement according to claim 9 wherein said vibrating means further includes a weight engaged with said spring, said weight being carried by said frame for vertical movement relative thereto. 

1. In a vibratory screed assembly for a paver or the like, the improvement comprising: a. a frame; b. a screed having leading and trailing portions; c. mounting means connecting the trailing portion of the screed with the frame for relative vibratory movement therebetween, said mounting means being defined by spring means which serve as the sole means for transferring draft forces from the frame to the screed; d. vibrating means connected to the leading portion of the screed; e. said mounting means and said vibrating means cooperating with each other to impart vibratory motion to the screed characterized by:
 1. at least vertical oscillatory movement of the leading portion of the screed;
 2. predominantly horizontal longitudinal movement of the trailing portion of the screed; whereby the amount of vertical vibratory movement of the screed progressively decreases from the leading portion to the trailing portion thereof.
 2. predominantly horizontal longitudinal movement of the trailing portion of the screed; whereby the amount of vertical vibratory movement of the screed progressively decreases from the leading portion to the trailing portion thereof.
 2. In a vibratory screed assembly for a paver or the like, the improvement comprising: a. a frame; b. a screed having leading and trailing portions; c. mounting means connecting the trailing portion of the screed to the frame, said mounting means being defined by yieldable means which are substantially inextensible in a vertical direction and which therefore permit movement of the trailing portion of the screed in a horizontal plane and restrain movement of said trailing portion in a vertical plane; d. vibrating means engaged with the screed adjacent the leading portion thereof; e. said mounting means and said vibrating means cooperating with each other to impart vibratory motion to the screed characterized by:
 2. orbital movement of the trailing portion of the screed as considered in a vertical longitudinal plane, the amount of vertical vibratory movement of the trailing portion of the screed being substantially less than the amount of vertical vibratory movement of the leading portion of the screed; whereby the amount of vertical vibratory movement of the screed progressively decreases from the leading portion to the trailing portion thereof.
 3. The improvement according to claim 2 wherein said vibrating means includes a vibratory mechanism mounted on the leading portion of the screed and including an eccentric elemenT supported for rotation about a horizontal transverse axis, and spring means engaged with said vibrating mechanism for transferring a vertical downward force to the latter.
 4. The improvement according to claim 3 wherein said vibrating means further includes a weight engaged with said spring, said weight being carried by said frame for vertical movement relative thereto.
 5. The improvement according to claim 2 wherein said yieldable means include plural leaf springs generally disposed in a vertical transverse plane, said springs having their upper ends fixed to said frame and their lower ends connected to the trailing portion of the screed by transverse horizontal pivot means.
 6. In a vibratory screed assembly for a paver or the like, the improvement comprising: a. a frame; b. a screed having leading and trailing portions; c. mounting means connecting the trailing portion of the screed to the frame and permitting at least rocking movement of the screed about a horizontal transverse axis disposed adjacent said trailing portion, said mounting means being defined by spring means which serve as the sole means for transferring draft forces from the frame to the screed; d. vibrating means connected to the leading portion of the screed; e. said mounting means and said vibrating means cooperating with each other to impart vibratory rocking movement of said screed about said axis, whereby the amount of vertical vibratory movement of the screed progressively decreases from the leading portion to the trailing portion thereof.
 7. The improvement according to claim 6 wherein said mounting means engages said screed adjacent only the trailing portion thereof and constitutes the sole means through which longitudinal draft forces are transferred from said frame to said screed.
 8. The improvement according to claim 7 wherein said vibratory means engages said screed adjacent only the leading portion thereof.
 9. The improvement according to claim 8 wherein said vibrating means includes a vibratory mechanism mounted on the leading portion of the screed and including an eccentric element supported for rotation about a horizontal transverse axis, and spring means engaged with said vibrating mechanism for transferring a vertical downward force to the latter.
 10. The improvement according to claim 9 wherein said vibrating means further includes a weight engaged with said spring, said weight being carried by said frame for vertical movement relative thereto. 